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A.H. Penninks, L.M.J.Knippels
Experimental Immunology, Division of Toxicology, TNO Nutrition and Food Research, P.O. Box 360, 3700 AJ Zeist , The Netherlands
At the time that the ILSI/IFBC decision tree approach was proposed for the“ Assessment of the Allergenic Potential of Foods derived from Genetically Modified Crop Plants” (Taylor et al., 1996) the need of accepted animal models was already clear. This has become even more evident following the recommendations in the recently released FAO/WHO 2001 report (FAO/WHO, 2001). This FAO/WHO expert consultation is of the opinion that animal models, though still in development, can provide informative data upon validation as they will be able to show the sensitising potency of new protein(s), relative to weak or strong known allergens. This was supported further by a Codex Ad Hoc Open-Ended working group on Allergenicity (Vancouver, September 2001). However, they suggested that animal models first required further development before they can be used to enhance the weight of evidence that will be used for decision making concerning potential allergenicity of a new food protein. The other criteria, and their limitations, currently used in the FAO/WAO 2001 decision tree approach will also be presented shortly.
Despite increasing research efforts in recent years to develop suitable animal models no validated and widely accepted animal model is yet available. These models should preferably mimic the induction of an IgE antibody response, as the most remarkable marker of allergic sensitisation, and the induction of symptoms upon a challenge reaction like observed in human allergic patients. In this presentation some new animal models will be introduced that have become available in literature and that currently are in further development for testing the allergenicity of new foods or food proteins, either or not derived by biotechnology. For food allergy research, three rodent species have frequently be used, viz. guinea pigs, mice and rats. As several drawbacks exist for the further use of guinea pigs in food allergy research, most attention is currently given to mice and rats, the latter two species being subject of this presentation.
In the past oral protein administration studies in mice (diet/gavage/drinking water) without using adjuvants easily resulted in tolerance induction. However, more recent studies in mice, using repeated enteral protein administration in combination with adjuvants, have shown that immune priming or sensitization can be achieved (Li et al., 1999; Li et al., 2000). In these studies allergic sensitisation of mice to cow’s milk and to peanut proteins could be induced upon oral application using cholera toxin as oral adjuvant. In studies of Ito et al.(1997), using oral sensitisation of mice by feeding casein or ovalbumin as a constituent in the diet (without adjuvant administration) allergic sensitisation was only observed with casein. Also the intraperitoneal route of exposure is studied in mice to assess the potential allergenicity of new proteins. These studies are focussed on both the antigenicity and allergenicity of these test proteins. The studies of Dearman et al.(2000), using ovalbumin (allergenic protein) and bovine serum albumin (limited allergenic protein) indicate, that characteristic antibody (IgG and IgE) isotype profiles can be provoked by proteins which may be associated with variable allergenic activity.
Also in rats the oral sensitization to food proteins has been studied by administration through the diet or by gavage-dosing either in the presence (Atkinson et al., 1996) or absence (Knippels et al., 1998a,b; 1999a,b; 2000) of an adjuvant. In this presentation the results of our studies are further summarized concerning the development of an oral sensitization protocol for food proteins in the BN rat. Results will be presented of oral sensitisation studies in young BN rats exposed to whole foods (cow’s milk), total protein extracts (hen’s egg-white, peanut) or purified strong or weak allergenic proteins (e.g ovalbumin, Ara h1 from peanut, tropomyosin from shrimp and beef, and patatin from potatoes) upon daily gavage dosing for 42 days without the use of an adjuvant.
Next to the possibilities attention will also be given to the limitations of the currently available models. Once validated these models to identify the potential allergenicity of novel proteins can of course also be used for more mechanistic research on food allergy and the development of new interventions for prophylaxis and therapy.
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